Pond Liner Calculator

Calculate the exact liner size, pond volume, and pump requirements for your garden pond — rectangle, oval, or irregular shapes.

Pond Dimensions

Pond Shape

Length (ft)

Width (ft)

Max Depth (ft)

Edge Overlap (inches)

Overlap goes over the edge and buries into soil — 12 in recommended.

Liner Size Needed

— × — ft

includes 12 in edge overlap on all sides

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Liner Sq Ft

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Pond Gallons

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Pump GPH Range

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Avg Depth

Nearest Standard Liner Size

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Water Volume Details

Full volume calculations and pump sizing for your pond.

Pump & Filter Sizing

Volume vs Depth

Pond Liner Material Comparison

Choose the right liner material based on durability, fish safety, and budget.

Best for Fish & Koi

EPDM 45 mil is the gold standard for koi ponds — fish-safe, flexible in cold temps, and highly puncture-resistant. Avoid PVC for fish ponds unless certified fish-safe.

Budget Option

PVC 20 mil works for smaller decorative ponds with no fish. It costs less per sq ft but is less UV-stable and more prone to cracking in cold climates.

Large & Commercial

HDPE is best for large ponds and farm applications. It is chemically resistant and extremely durable but requires professional installation due to its rigidity.

Preformed Shells

Rigid preformed shells are easiest to install and longest-lasting, but size and shape options are limited. Best for small decorative ponds up to ~200 gallons.

Pond Liner Installation Guide

Step-by-step installation process for a flexible liner pond.

Pro Tips

Always install liner on a warm day (above 60°F) — EPDM softens and becomes more pliable in warm weather, making it easier to fold and position.
Use pond underlayment (felt geotextile) under the liner to prevent punctures from sharp stones or roots — never skip this step.
Fold pleats evenly around curves rather than cutting — seams are weak points. One continuous sheet is always better than patched pieces.
Leave the liner loose during filling — the water weight will pull it into contours naturally. Anchor the perimeter after the pond is half full.
Dechlorinate tap water before introducing fish — use sodium thiosulfate or commercial pond dechlorinator per label. Let the pond cycle 2–4 weeks before adding fish.

How to Use This Calculator

Select your pond shape — Choose Rectangle for a standard box pond, Oval for an egg-shaped design, or Irregular for an organic free-form shape (uses the same formula with added margin).

Enter pond length and width — Measure the longest points of your planned pond in feet. For oval ponds, enter the maximum length and width across the widest points.

Enter max depth — The deepest point of your pond. Volume uses 75% of max depth as the average to account for sloped sides.

Set edge overlap — The liner extends beyond the edge and buries into soil. 12 inches is the minimum; 18 inches is recommended for edging with large stones.

Read the liner size — The hero value shows the exact liner dimensions you need to order. Always buy the nearest standard size that is larger.

Check Volume & Pump tab — Review pump GPH requirements to ensure good water circulation for healthy pond biology.

Pond Liner Terminology

EPDMEthylene Propylene Diene Monomer — a synthetic rubber liner; most common choice for garden ponds. 45 mil is the pond-grade thickness.

MilOne thousandth of an inch (0.001 in). Liner thickness is measured in mils — 45 mil EPDM = 0.045 inches thick.

Edge OverlapThe portion of liner that extends beyond the pond edge and is buried under soil, rocks, or turf to anchor the liner and prevent it pulling into the water.

Turnover RateThe number of times the full pond volume passes through the pump and filter per hour. 1–2 turnovers/hr is recommended for healthy water quality.

UnderlaymentFelt geotextile fabric placed under the liner to protect it from puncture by sharp rocks, roots, or rough soil.

GPHGallons Per Hour — the flow rate rating of a pond pump. Always match pump GPH to 1–2× your pond volume.

Fish-Safe LinerA liner certified free of plasticizers, UV stabilizers, and biocides that can leach into water and harm fish. EPDM 45 mil is inherently fish-safe; not all PVC liners are.

DechlorinationRemoving chlorine and chloramine from tap water before introducing fish. Required any time new tap water is added to the pond.

Frequently Asked Questions

How do I measure an irregular pond shape?

For an irregular or free-form pond, measure the longest length and widest width as if the pond were inscribed in a rectangle. The calculator adds the full edge overlap to all four sides, giving you enough liner to work with. For very complex shapes with deep notches, add 10–15% extra to the liner dimensions as a buffer.

What liner thickness should I buy?

For most garden ponds: EPDM 45 mil. For small decorative ponds without fish: PVC 20–30 mil is acceptable. For large or commercial ponds: HDPE 40–60 mil. Never go below 20 mil — thin liners puncture easily and have short UV lifespans. EPDM 45 mil carries a typical 20-year warranty.

How much overlap do I need?

The minimum recommended overlap is 12 inches (1 foot) on all sides. If you plan to edge with large boulders or heavy stone (which may shift and stress the liner), increase overlap to 18–24 inches. More overlap is always better — you can trim excess but you cannot add length after installation.

What pump size do I need for a koi pond?

For koi ponds, size the pump to turn over the entire pond volume at least once per hour — some koi keepers prefer 2× per hour for heavy stocking. Also size the biological filter at 2× the pump flow rate (e.g., a 1,000 GPH pump needs a filter rated for 2,000 GPH). Koi produce significantly more waste than goldfish or ornamental fish.

Can I join two liner pieces together?

Yes, EPDM liners can be joined with specialized EPDM splice tape or liquid primer/bonding adhesive made for rubber liners. Seams should overlap 3–6 inches and must be fully dry and clean before bonding. However, a single-piece liner with no seams is always preferable — seams are a potential leak point even when done correctly.